1. Field of the Invention
The present invention relates generally to an automobile air conditioner system, and more particularly to such system having a temperature control device for adjusting the opening position of an air-mix door in the air conditioner system to control the temperature of air blown into a vehicle passenger compartment.
2. Prior Art
Japanese Utility Model Laid-open Publication No. 59-75797 discloses one such automobile air conditioner system which comprises, as shown in FIG. 4 of the accompanying drawings, an air-mix door 3 disposed in an air duct 1 immediately upstream of a heater core 2 to proportion the amount of air flow passing through the heater core 2 and the amount of air flow by-passing the heater core 2, thereby controlling the temperature of air which is introduced into a vehicle passenger compartment. Thus, the air temperature t blown-off from the duct 1 is determined in accordance with the opening position or amount 0 of the air-mix door 3. The air-mix door 3 is connected to a drive shaft 6 of a motor actuator 5 via a linkage mechanism 4. The motor actuator 5 includes a motor 8 driven by a control circuit 7 to turn the drive shaft 6 in response to an output signal from the control circuit 7. The motor actuator 5 further includes a potentiometer 9 for detecting the opening amount of the air-mix door 3. The potentiometer 9 includes a movable contact 9a movable in unison with the air-mix door 3, and a resistance element 9b along which the movable contact 9a slides such that the output voltage at the movable contact 9a is a linear function of the displacement of the contact with various sensors such as a temperature setter 10, a compartment air temperature sensor 11, an outside air temperature sensor 12 and a sunlit-portion temperature sensor 13 to receive therefrom input information concerning thermal loads on the air conditionner system. On the basis of the input information, the control circuit then computes a composite signal corresponding to the thermal loads. The composite signal is compared with the signal delivered from the potentiometer 9 and indicative of the opening amount of the air-mix door 3 so as to determine a control signal which is in turn fed back to the motor 8 to control the same.
The blown-off air temperature t of the temperature control system occasionally varies out of linear function of the opening amount .theta. of the air-mix door 3. More specifically, as shown in FIG. 5, as the air-mix door 3 approaches its full hot position, the blown-off air temperature t shows an irregular change with respect to an even increase in the opening amount .theta. of the air-mix door 3. Occurence of such phenomenon depends upon the structure of the duct 1 or the location of the heater core 2.
If the opening amount .theta. of the air-mix door 3 were linearly related to the output voltage of the potentiometer 9, the control circuit 7 would produce output signals to move the air-mix door 3 toward the HOT side for effecting a uniform increase .DELTA..theta..sub.2 in the opening amount .theta., thereby increasing the blown-off air temperature t by the amount .DELTA.t.sub.2. With this arrangement, the desired preset temperature is obtainable when the opening amount .theta. of the air-mix door 3 is below a value .theta..sub.1. However, when the opening amount .theta. exceeds the value .theta..sub.1, a change or variation .DELTA.t2', becomes greater than the change .DELTA.t.sub.2 and deviates from the present temperature. As a result, confortable air conditioning of the vehicle passenger compatment is difficult to achieve.